Valve timing control apparatus for internal combustion engine

ABSTRACT

A valve timing control apparatus for an internal combustion engine includes a variable valve timing control mechanism of a hydraulic type which is provided in a drive force transmission arrangement for transmitting a drive force from a driving shaft to a driven shaft for actuating one of an engine-cylinder inlet valve and an engine-cylinder outlet valve, and which can relatively rotate one of the driving shaft and the driven shaft in a predetermined angular range. A detecting device operates for detecting a condition in which air enters hydraulic working fluid in the variable valve timing control mechanism. A trouble diagnosis device operates for implementing a trouble diagnosis on the variable valve timing control mechanism. An inhibiting device operates for inhibiting the trouble diagnosis implemented by the trouble diagnosis device when the detecting device detects the condition in which air enters hydraulic working fluid in the variable valve timing control mechanism.

This is a divisional of application Ser. No. 09/150,029, filed Sep. 9,1998, the entire content of which is hereby incorporated by reference inthis application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a valve timing control apparatus foran internal combustion engine. This invention particularly relates to anapparatus for controlling the opening and closing timings of at leastone of an inlet valve and an outlet valve in each engine cylinder inresponse to an operating condition of an internal combustion engine.

2. Description of the Related Art

A known valve timing control apparatus for an internal combustion engineincludes a variable valve timing control mechanism which has ahydraulically-controllable cam pulley connected to a camshaft. The campulley can vary a cam phase difference relative to crank angle. Thevariation in the cam phase difference causes a variation in the openingand closing timings of, for example, an inlet valve of each enginecylinder. Generally, the valve timing is adjusted in response to therotational speed of the engine or the load on the engine.

Regarding the variable valve timing control mechanism, it is known toprovide a system for diagnosing a trouble in its operation by referringto the pressure of used hydraulic fluid. It is difficult for such adiagnosis system to detect a trouble which does not cause anyabnormality in the hydraulic pressure.

Japanese patent 2590384 discloses a variable valve timing controlmechanism provided with a system which diagnoses a trouble in itsoperation by referring to the phase difference between an enginecrankshaft and an engine camshaft.

In a variable valve timing control mechanism of the hydraulic type, ifair enters the hydraulic working fluid, the pressure of the fluid tendsto be insufficient due to an easy variation in volume of the air. Theinsufficient hydraulic pressure impairs operation of the variable valvetiming control mechanism. In addition, such an insufficient hydraulicpressure may be diagnosed as a trouble in the variable valve timingcontrol mechanism.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a valve timing controlapparatus for an internal combustion engine which can accuratelydiagnose a trouble in operation of a variable valve timing controlmechanism.

A first aspect of this invention provides a valve timing controlapparatus for an internal combustion engine which comprising a variablevalve timing control mechanism of a hydraulic type which is provided ina drive force transmission arrangement for transmitting a drive forcefrom a driving shaft to a driven shaft for actuating one of anengine-cylinder inlet valve and an engine-cylinder outlet valve, andwhich can relatively rotate one of the driving shaft and the drivenshaft in a predetermined angular range; detecting means for detecting acondition in which air enters hydraulic working fluid in the variablevalve timing control mechanism; trouble diagnosis means for implementinga trouble diagnosis on the variable valve timing control mechanism; andinhibiting means for inhibiting the trouble diagnosis implemented by thetrouble diagnosis means when the detecting means detects the conditionin which air enters hydraulic working fluid in the variable valve timingcontrol mechanism.

A second aspect of this invention is based on the first aspect thereof,and provides a valve timing control apparatus further comprising drivingshaft rotational angle detecting means for detecting a rotational angleof the driving shaft; driven shaft rotational angle detecting means fordetecting a rotational angle of the driven shaft; relative rotationalangle calculating means for calculating an actual relative rotationalangle which is equal to an actual phase difference between therotational angle of the driving shaft which is detected by the drivingshaft rotational angle detecting means and the rotational angle of thedriven shaft which is detected by the driven shaft rotational angledetecting means; engine operating condition detecting means fordetecting an operating condition of the engine; target relativerotational angle calculating means for calculating a target relativerotational angle which is equal to a target phase difference between therotational angle of the driving shaft and the rotational angle of thedriven shaft in response to the operating condition of the engine whichis detected by the engine operating condition detecting means; controlrotational angle calculating means for calculating a control rotationalangle in response to a difference between the actual relative rotationalangle calculated by the relative rotational angle calculating means andthe target relative rotational angle calculated by the target relativerotational angle calculating means; and relative rotational anglecontrol means for controlling the variable valve timing controlmechanism to relatively rotate one of the driving shaft and the drivenshaft in response to the control rotational angle calculated by thecontrol rotational angle calculating means.

A third aspect of this invention provides a valve timing controlapparatus for an internal combustion engine which comprises a variablevalve timing control mechanism of a hydraulic type which is provided ina drive force transmission arrangement for transmitting a drive forcefrom a driving shaft to a driven shaft for actuating one of anengine-cylinder inlet valve and an engine-cylinder outlet valve, andwhich can relatively rotate one of the driving shaft and the drivenshaft in a predetermined angular range; driving shaft rotational angledetecting means for detecting a rotational angle of the driving shaft;driven shaft rotational angle detecting means for detecting a rotationalangle of the driven shaft; relative rotational angle calculating meansfor calculating an actual relative rotational angle which is equal to anactual phase difference between the rotational angle of the drivingshaft which is detected by the driving shaft rotational angle detectingmeans and the rotational angle of the driven shaft which is detected bythe driven shaft rotational angle detecting means; engine operatingcondition detecting means for detecting an operating condition of theengine; target relative rotational angle calculating means forcalculating a target relative rotational angle which is equal to atarget phase difference between the rotational angle of the drivingshaft and the rotational angle of the driven shaft in response to theoperating condition of the engine which is detected by the engineoperating condition detecting means; control rotational anglecalculating means for calculating a control rotational angle in responseto a difference between the actual relative rotational angle calculatedby the relative rotational angle calculating means and the targetrelative rotational angle calculated by the target relative rotationalangle calculating means; relative rotational angle control means forcontrolling the variable valve timing control mechanism to relativelyrotate one of the driving shaft and the driven shaft in response to thecontrol rotational angle calculated by the control rotational anglecalculating means; detecting means for detecting a condition in whichair enters hydraulic working fluid in the variable valve timing controlmechanism; and relative rotational angle correcting means for correctingthe target relative rotational angle toward a retarded angle side whenthe detecting means detects the condition in which air enters hydraulicworking fluid in the variable valve timing control mechanism.

A fourth aspect of this invention is based on the first aspect thereof,and provides a valve timing control apparatus wherein the condition inwhich air enters hydraulic working fluid in the variable valve timingcontrol mechanism is in a predetermined time interval within or afterhigh rotational speed operation of the engine.

A fifth aspect of this invention is based on the first aspect thereof,and provides a valve timing control apparatus wherein the condition inwhich air enters hydraulic working fluid in the variable valve timingcontrol mechanism corresponds to turn of a vehicle powered by theengine.

A sixth aspect of this invention is based on the first aspect thereof,and provides a valve timing control apparatus wherein the condition inwhich air enters hydraulic working fluid in the variable valve timingcontrol mechanism is set on the basis of a behavior of a pressure ofhydraulic working fluid.

A seventh aspect of this invention is based on the first aspect thereof,and provides a valve timing control apparatus wherein the condition inwhich air enters hydraulic working fluid in the variable valve timingcontrol mechanism corresponds to travel of a vehicle powered by theengine on a rough road.

An eighth aspect of this invention provides a control apparatus for aninternal combustion engine which comprises a valve timing controlapparatus for controlling at least one of a valve lift amount, a valvetiming related to an engine-cylinder inlet valve, and a valve timingrelated to an engine-cylinder outlet valve; malfunction detecting meansfor detecting malfunction of the valve timing control apparatus; andfail-safe means for implementing fail safe on the engine when themalfunction detecting means detects malfunction of the valve timingcontrol apparatus.

A ninth aspect of this invention is based on the eighth aspect thereof,and provides a control apparatus further comprising second malfunctiondetecting means for detecting malfunction of a second apparatus providedon the engine which is affected by malfunction of the valve timingcontrol apparatus, and inhibiting means contained in the fail-safe meansfor inhibiting the second malfunction detecting means from detectingmalfunction of the second apparatus.

A tenth aspect of this invention is based on the ninth aspect thereof,and provides a control apparatus wherein the second malfunctiondetecting means comprises means for detecting misfire in the engine.

An eleventh aspect of this invention is based on the ninth aspectthereof, and provides a control apparatus wherein the second malfunctiondetecting means comprises means for detecting malfunction of a fuelsupply apparatus.

A twelfth aspect of this invention is based on the ninth aspect thereof,and provides a control apparatus wherein the second malfunctiondetecting means comprises means for detecting malfunction of one of afront O₂ sensor and a rear O₂ sensor.

A thirteenth aspect of this invention is based on the ninth aspectthereof, and provides a control apparatus wherein the second malfunctiondetecting means comprises means for detecting deterioration of acatalytic converter.

A fourteenth aspect of this invention is based on the ninth aspectthereof, and provides a control apparatus wherein the second malfunctiondetecting means comprises means for detecting malfunction of a fuelvapor treating apparatus.

A fifteenth aspect of this invention is based on the eighth aspectthereof, and provides a control apparatus further comprising feedbackcontrol means for implementing knock-based feedback control of a sparktiming in the engine; inhibiting means contained in the fail-safe meansfor inhibiting the feedback control means from implementing theknock-based feedback control of the spark timing; and spark timingcontrol means contained in the fail-safe means for setting the sparktiming to a first timing when the malfunction detecting means detectsmalfunction of the valve timing control apparatus, the first timingbeing retarded from a second timing to which the spark timing is setwhen the malfunction detecting means does not detect malfunction of thevalve timing control apparatus.

A sixteenth aspect of this invention is based on the ninth aspectthereof, and provides a control apparatus further comprisinginvalidating means for invalidating a result of the detecting by thesecond malfunction detecting means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an internal combustion engine of the double overhead camshaft type, and a valve timing control apparatus according to afirst embodiment of this invention.

FIG. 2 is a flowchart of a segment of a program for an electroniccontrol unit in FIG. 1.

FIG. 3 is a diagram of a table map which indicates a predeterminedrelation among a target rotational angle AVTT, a rotational engine speedNE (rpm), and an intake manifold pressure PM (kgf/cm²).

FIG. 4 is a flowchart of a segment of a program for an electroniccontrol unit in a second embodiment of this invention.

FIG. 5 is a flowchart of a segment of a program for an electroniccontrol unit in a third embodiment of this invention.

FIG. 6 is a flowchart of a segment of a program for an electroniccontrol unit in a fourth embodiment of this invention.

FIG. 7 is a diagram of a map which indicates a predetermined relationbetween a target hydraulic pressure TPOILUP and a rotational enginespeed NE.

FIG. 8 is a flowchart of a segment of a program for an electroniccontrol unit in a fifth embodiment of this invention.

FIG. 9 is a diagram of an internal combustion engine of the double overhead camshaft type, a valve timing control apparatus, and an enginecontrol apparatus according to a sixth embodiment of this invention.

FIG. 10 is a flowchart of a first segment of a program for an electroniccontrol unit in FIG. 9.

FIG. 11 is a diagram of a table map which indicates a predeterminedrelation among a target rotational angle AVTT, a rotational engine speedNE, and an air flow rate GN.

FIG. 12 is a diagram of a map which indicates a predetermined relationbetween a control rotational angle DVFB and a rotational angledifference "AVTT-AVTA".

FIG. 13 is a diagram of a relation between a rate of hydraulic fluidflow into a variable valve timing control mechanism and a desired dutycycle DV or a basic duty value DVT.

FIG. 14 is a flowchart of a second segment of the program for theelectronic control unit in FIG. 9.

FIG. 15 is a flowchart of a third segment of the program for theelectronic control unit in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

With reference to FIG. 1, a valve timing control apparatus of a firstembodiment of this invention operates for an internal combustion engine10 having a crankshaft 11 which serves as a driving shaft with respectto a variable valve timing control mechanism 50. The valve timingcontrol apparatus contains the variable valve timing control mechanism50.

The crankshaft 11 is connected to a pair of chain sprockets 13 and 14via a chain 12 in the valve timing control apparatus. A drive force canbe transmitted from the crankshaft 11 to the chain sprockets 13 and 14.As the crankshaft 11 rotates, the chain sprockets 13 and 14 also rotate.Generally, the rotational speed of the chain sprockets 13 and 14 isequal to half the speed of rotation of the crankshaft 11. The chainsprocket 13 is connected to a camshaft 15 for driving engine-cylinderinlet valves (not shown). Normally, the camshaft 15 rotates togetherwith the chain sprocket 13. The camshaft 15 serves as a driven shaftwith respect to the variable valve timing control mechanism 50. Thechain sprocket 14 is mounted on a camshaft 16 for drivingengine-cylinder outlet valves (not shown). The camshaft 16 rotatestogether with the chain sprocket 14.

A crankshaft position sensor 21 is associated with the crankshaft 11.The crankshaft position sensor 21 outputs a pulse signal θ1 representingthe angular position of the crankshaft 11. A camshaft position sensor 22is associated with the camshaft 15. The camshaft position sensor 22outputs a pulse signal θ2 representing the angular position of thecamshaft 15.

An electronic control unit (ECU) 30 receives the output signals θ1 andθ2 of the crankshaft position sensor 21 and the camshaft position sensor22. The ECU 30 includes a microcomputer or a logic operation circuithaving a combination of a CPU, a ROM, a general RAM, a backup RAM, aninput/output port, and bus lines. The ECU 30 operates in accordance witha program stored in the ROM.

An air pressure sensor (not shown) detects the intake air pressure orthe intake manifold pressure in the engine 10, that is, the pressure ina region of an air induction passage (an air intake passage) of theengine 10 downstream of an engine throttle valve. The ECU 30 receives anoutput signal of the air pressure sensor which represents the detectedintake manifold pressure.

A temperature sensor (not shown) detects the temperature of coolant inthe engine 10. The ECU 30 receives an output signal of the temperaturesensor which represents the detected engine coolant temperature.

The ECU 30 calculates an actual rotational angle AVTA of the camshaft 15relative to the crankshaft 11 on the basis of the output signals θ1 andθ2 of the crankshaft position sensor 21 and the camshaft position sensor22. In addition, the ECU 30 calculates a target rotational angle AVTT ofthe camshaft 15 relative to the crankshaft 11 on the basis of the outputsignals of sensors including the crankshaft position sensor 21 and theair pressure sensor. Furthermore, the ECU 30 calculates the rotationalengine speed NE, that is, the speed of rotation of the crankshaft 11 onthe basis of the output signal θ1 of the crankshaft position sensor 21.

A spool valve 40 which serves as an oil-flow control valve (OCV) can beactuated by a linear solenoid 41. The spool valve 40 is disposed inhydraulic passages extending among a tank 45, a pump 46, and thevariable valve timing control mechanism (VVT) 50. The tank 45 containshydraulic fluid. The pump 46 draws hydraulic fluid from the tank 45, andpumps hydraulic fluid toward the VVT 50 via a fluid feed passage 47 andthe spool valve 40. The state or the position of the spool valve 40 iscontrolled by the linear solenoid 41. The spool valve 40 can adjust therate of hydraulic-fluid flow to the VVT 50 in response to the duty cycleor the duty factor of a drive pulse signal applied to the linearsolenoid 41. The VVT 50 is provided between the chain sprocket 13 andthe camshaft 15. The VVT 50 varies the angular difference (the phasedifference) between the sprocket 13 and the camshaft 15, that is, therotational angle of the camshaft 15 relative to the crankshaft 11 inresponse to hydraulic fluid fed via the spool valve 40. Hydraulic fluidcan return from the VVT 50 to the tank 45 via the spool valve 40 and afluid return passage 48.

The ECU 30 calculates the difference between the actual rotational angleAVTA and the target rotational angle AVTT of the camshaft 15 relative tothe crankshaft 11. The ECU 30 generates a fixed-frequency drive pulsesignal for the linear solenoid 41 which has a duty cycle or a dutyfactor depending on the calculated difference between the actualrotational angle AVTA and the target rotational angle AVTT of thecamshaft 15 relative to the crankshaft 11. Thereby, the actualrotational angle AVTA of the camshaft 15 relative to the crankshaft 11can be equalized to the target rotational angle AVTT thereof.

A hydraulic pressure sensor 49 is disposed in a region of the fluid feedpassage 47 downstream of the pump 46. The hydraulic pressure sensor 49detects the pressure of hydraulic fluid transmitted from the pump 46toward the VVT 50. In other words, the hydraulic pressure sensor 49detects the pressure of hydraulic fluid at the outlet of the pump 46.The hydraulic pressure sensor 49 outputs a signal to the ECU 30 whichrepresents the detected hydraulic pressure Poil.

The engine 10 drives a vehicle provided with a power steering switch(not shown). When a vehicle steering wheel is out of its neutralposition, the power steering switch is in its ON position. When thevehicle steering wheel is in its neutral position, the power steeringswitch is in its OFF position. The power steering switch outputs asignal to the ECU 30 which represents the current position thereof.

The vehicle has a body provided with a vehicle speed sensor (not shown)for detecting the speed of the vehicle body. The vehicle speed sensoroutputs a signal to the ECU 30 which represents the detected vehiclespeed.

A warning lamp (not shown) is located in the interior of the vehicle.The warning lamp is connected to the ECU 30. The warning lamp can beactivated and deactivated by the ECU 30.

The crankshaft position sensor 21 and the camshaft position sensor 22are designed to implement the following processes. During everyrevolution of the crankshaft 11, N pulses are successively outputtedfrom the crankshaft position sensor 21. Here, N denotes a predeterminednatural number. During every revolution of the camshaft 15, N pulses aresuccessively outputted from the camshaft position sensor 22. The numberN is chosen to satisfy a condition as "N<360/θmax" where θmax denotesthe maximum value of timing conversion related to the camshaft 15 whichis expressed in unit of degree in crank angle (CA). Accordingly, a pulsein the output signal θ1 of the crankshaft position sensor 21, and apulse in the output signal θ2 of the camshaft position sensor 22 whichoccurs immediately after the pulse in the signal θ1 can be used incalculating the actual rotational angle AVTA of the camshaft 15 relativeto the crankshaft 11.

As previously explained, the ECU 30 operates in accordance with aprogram stored in its internal ROM. FIG. 2 is a flowchart of a segment(routine) of the program which is designed to diagnose a trouble in or afailure of the VVT 50. In the case where the engine 10 has fourcylinders, the program segment in FIG. 2 is executed for every 180° CA(crank angle).

As shown in FIG. 2, a first step S101 of the program segment clears thevariable CVDTA to "0". The variable CVDTA is used as an indication ofthe time of continuation or the duration of wrong operation of the VVT50. After the step S101, the program advances to a step S102.

The step S102 reads the current states of the output signals θ1 and θ2of the crankshaft position sensor 21 and the camshaft position sensor22. The step S102 reads the current state of the output signal of thepower steering switch. The step S102 reads the current value of therotational engine speed NE (rpm). The step S102 derives the currentvalue of the intake manifold pressure PM (kgf/cm²) from the outputsignal of the air pressure sensor. The step S102 derives the currentvalue of the vehicle speed from the output signal of the vehicle speedsensor.

A step S103 following the step S102 calculates the actual rotationalangle AVTA of the camshaft 15 relative to the crankshaft 11 from thecurrent states of the output signals θ1 and θ2 of the crankshaftposition sensor 21 and the camshaft position sensor 22 by referring toan equation as "AVTA=θ1-θ2".

A step S104 subsequent to the step S103 calculates the target rotationalangle AVTT of the camshaft 15 relative to the crankshaft 11 from thecurrent rotational engine speed NE (rpm) and the current intake manifoldpressure PM (kgf/cm²).

The ROM in the ECU 30 stores information of a table map which indicatesa predetermined relation among the target rotational angle AVTT, therotational engine speed NE (rpm), and the intake manifold pressure PM(kgf/cm²). An example of the table map is shown in FIG. 3. The step S104implements the calculation of the target rotational angle AVTT byreferring to the table map in FIG. 3.

A step S105 following the step S104 decides whether or not the powersteering switch is in its ON position, that is, whether or not thevehicle steering wheel is out of its neutral position, by referring tothe current state of the output signal thereof. When it is decided thatthe power steering switch is in its ON position, that is, when it isdecided that the vehicle steering wheel is out of its neutral position,the program advances from the step S105 to a step S106. Otherwise, theprogram advances from the step S105 to a step S107.

The step S106 decides whether or not the current vehicle speed exceeds apredetermined reference speed KVCIR. When it is decided that the currentvehicle speed exceeds the reference speed KVCIR, the program exits fromthe step S106 and then the current execution cycle of the programsegment ends. When it is decided that the current vehicle speed does notexceed the reference speed KVCIR, the program advances from the stepS106 to the step S107.

Accordingly, in the case where the vehicle is turning and is moving at aspeed higher than the reference speed KVCIR, main program steps for atrouble diagnosis on the VVT 50 remain unexecuted. It should be notedthat under these vehicle operating conditions, there is a chance of theentry of air into hydraulic fluid in the VVT 50.

The step S107 calculates the absolute value |AVTT-AVTA| of thedifference between the actual rotational angle AVTA and the targetrotational angle AVTT which have been given by the steps S103 and S104.The step S107 decides whether or not the absolute value |AVTT-AVTA| ofthe difference exceeds a predetermined reference angular value KVDTA.When it is decided that the absolute value |AVTT-AVTA| of the differenceexceeds the reference angular value KVDTA, the program advances from thestep S107 to a step S108. In this case, it is thought that operation ofthe VVT 50 is wrong. When it is decided that the absolute value|AVTT-AVTA| of the difference does not exceed the reference angularvalue KVDTA, the program returns from the step S107 to the step S101. Inthis case, it is thought that operation of the VVT 50 is good.

The step S108 increments the wrong-operation continuation time CVDTA by"1". After the step S108, the program advances to a step S109.

The step S109 decides whether or not the wrong-operation continuationtime CVDTA exceeds a predetermined reference time KTDTA. When it isdecided that the wrong-operation continuation time CVDTA exceeds thereference time KTDTA, the program advances from the step S109 to a stepS110. When it is decided that the wrong-operation continuation timeCVDTA does not exceed the reference time KTDTA, the program returns fromthe step S109 to the step S102.

The step S110 sets a flag for indicating that the VVT 50 fails. Inaddition, the step S110 activates the warning lamp. After the step S110,the current execution cycle of the program segment ends.

As previously mentioned, in the valve timing control apparatus of thefirst embodiment of this invention, the crankshaft 11 of the engine 10serves as the driving shaft with respect to the VVT 50. The camshaft 15for driving the engine-cylinder inlet valves serves as the driven shaftwith respect to the VVT 50. The drive force is transmitted from thecrankshaft 11 to the camshaft 15 by a drive-force transmissionarrangement including the chain 12 and the chain sprocket 13. The VVT 50is provided in the drive-force transmission arrangement. The VVT 50 canvary the rotational angle of the camshaft 15 relative to the crankshaft11 in a predetermined angular range. The crankshaft position sensor 21detects the angular position of the crankshaft 11. The camshaft positionsensor 22 detects the angular position of the camshaft 15. The ECU 30calculates the difference (the phase difference) between the angularpositions of the crankshaft 11 and the camshaft 15 which are detected bythe crankshaft position sensor 21 and the camshaft position sensor 22.The calculated phase difference agrees with the actual rotational angleAVTA of the camshaft 15 relative to the crankshaft 11. The ECU 30calculates the target rotational angle AVTT of the camshaft 15 relativeto the crankshaft 11 on the basis of the operating conditions of theengine 10. The ECU 30 calculates a desired drive force to the VTT 50 onthe basis of the difference between the target rotational angle AVTT andthe actual rotational angle AVTA. The desired drive force to the VTT 50is given as a desired control rotational angle. The ECU 30 controls theVTT 50 via the linear solenoid 41 in response to the difference betweenthe target rotational angle AVTT and the actual rotational angle AVTA tomove the actual rotational angle AVTA toward the target rotational angleAVTT. Thus, the VTT 50 is feedback-controlled to equalize the actualrotational angle AVTA and the target rotational angle AVTT. The ECU 30detects the presence and the absence of conditions under which air tendsto enter hydraulic fluid in the VVT 50. When the presence of suchconditions is detected, the ECU 30 inhibits the trouble diagnosis on theVTT 50 from being implemented.

If air enters hydraulic fluid in the VTT 50, the pressure of hydraulicfluid therein tends to be insufficient due to an easy variation involume of the air. It is possible to prevent such an insufficienthydraulic pressure from being diagnosed as a trouble in the feedbackcontrol of the VVT 50 since the ECU 30 inhibits the execution of thetrouble diagnosis on the VTT 50 in these conditions.

The valve timing control apparatus of the first embodiment of thisinvention may be modified so that the VTT 50 will not befeedback-controlled. According to this modification, the crankshaft 11of the engine 10 serves as the driving shaft with respect to the VVT 50.The camshaft 15 for driving the engine-cylinder inlet valves serves asthe driven shaft with respect to the VTT 50. The drive force istransmitted from the crankshaft 11 to the camshaft 15 by a drive-forcetransmission arrangement including the chain 12 and the chain sprocket13. The VVT 50 is provided in the drive-force transmission arrangement.The VVT 50 can vary the rotational angle of the camshaft 15 relative tothe crankshaft 11 in a predetermined angular range. The ECU 30 detectsthe presence and the absence of conditions under which air tends toenter hydraulic fluid in the VVT 50. When the presence of suchconditions is detected, the ECU 30 inhibits the trouble diagnosis on theVTT 50 from being implemented.

If air enters hydraulic fluid in the VTT 50, the pressure of hydraulicfluid therein tends to be insufficient due to an easy variation involume of the air. The above-mentioned modification can prevent such aninsufficient hydraulic pressure from being diagnosed as a trouble sincethe ECU 30 inhibits the execution of the trouble diagnosis on the VTT 50in these conditions.

In the valve timing control apparatus of the first embodiment of thisinvention, it is thought that the conditions under which air tends toenter hydraulic fluid in VVT 50 occur during turn of the vehicle. Infact, air tends to enter hydraulic fluid in the VVT 50 and the pressureof hydraulic fluid tends to be unstable during turn of the vehicle. Theexecution of the trouble diagnosis on the VVT 50 is inhibited duringturn of the vehicle. Thus, it is possible to prevent temporary wrongoperation of the VTT 50, which is caused by the entry of air intohydraulic fluid, from being diagnosed as a failure of the VTT 50 duringturn of the vehicle.

The valve timing control apparatus of the first embodiment of thisinvention decides that the vehicle is turning in the case where thepower steering switch is in its ON position and the current vehiclespeed exceeds the reference speed KVCIR. Turn of the vehicle may bedetected from other parameters such as the lateral acceleration of thevehicle body which is sensed by a lateral G sensor, the steering angleof the steering wheel, the rotational engine speed, and the engine load.

Second Embodiment

A second embodiment of this invention is similar to the first embodimentthereof except for design changes indicated later.

In the second embodiment of this invention, the ECU 30 operates inaccordance with a program stored in its internal ROM. FIG. 4 is aflowchart of a segment (routine) of the program which is designed tocorrect the target rotational angle AVIT of the camshaft 15 relative tothe crankshaft 11. In the case where the engine 10 has four cylinders,the program segment in FIG. 4 is executed for every 180° CA (crankangle).

As shown in FIG. 4, a first step S201 of the program segment reads thecurrent states of the output signals θ1 and θ2 of the crankshaftposition sensor 21 and the camshaft position sensor 22. The step S201reads the current state of the output signal of the power steeringswitch. The step S201 reads the current value of the rotational enginespeed NE (rpm). The step S201 derives the current value of the intakemanifold pressure PM (kgf/cm²) from the output signal of the airpressure sensor. The step S201 derives the current value of the vehiclespeed from the output signal of the vehicle speed sensor.

A step S202 following the step S201 calculates the target rotationalangle AVTT of the camshaft 15 relative to the crankshaft 11 from thecurrent rotational engine speed NE (rpm) and the current intake manifoldpressure PM (kgf/cm²) as the step S104 in FIG. 2 does.

A step S203 subsequent to the step S202 decides whether or not the powersteering switch is in its ON position, that is, whether or not thevehicle steering wheel is out of its neutral position, by referring tothe current state of the output signal thereof. When it is decided thatthe power steering switch is in its ON position, that is, when it isdecided that the vehicle steering wheel is out of its neutral position,the program advances from the step S203 to a step S204. Otherwise, theprogram advances from the step S203 to a step S206.

The step S204 decides whether or not the current vehicle speed exceedsthe reference speed KVCIR. When it is decided that the current vehiclespeed exceeds the reference speed KVCIR, the program advances from thestep S204 to a step S205. Otherwise, the program advances from the stepS204 to the step S206.

The step S205 sets a corrective coefficient KAVTT to a predeterminedvalue "α" smaller than 1.0. After the step S205, the program advances toa step S207.

The step S206 sets the corrective coefficient KAVTT to 1.0. After thestep S206, the program advances to the step S207.

The step S207 updates or corrects the target rotational angle AVTT inresponse to the corrective coefficient KAVITT by referring to a programstatement as "AVTT=AVTT•KAVTT". Thus, the step S207 determines thecorrection-resultant target rotational angle AVTT. Thecorrection-resultant target rotational angle AVTT will be used by thestep S107 in FIG. 2. After the step S207, the current execution cycle ofthe program segment ends.

Accordingly, in the case where the vehicle is turning and is moving at aspeed higher than the reference speed KVCIR, the target rotational angleAVIT is corrected by the steps S205 and S207 toward a retarded angleside.

In the valve timing control apparatus of the second embodiment of thisinvention, the crankshaft 11 of the engine 10 serves as the drivingshaft with respect to the VVT 50. The camshaft 15 for driving theengine-cylinder inlet valves serves as the driven shaft with respect tothe VVT 50. The drive force is transmitted from the crankshaft 11 to thecamshaft 15 by a drive-force transmission arrangement including thechain 12 and the chain sprocket 13. The VVT 50 is provided in thedrive-force transmission arrangement. The VVT 50 can vary the rotationalangle of the camshaft 15 relative to the crankshaft 11 in apredetermined angular range. The crankshaft position sensor 21 detectsthe angular position of the crankshaft 11. The camshaft position sensor22 detects the angular position of the camshaft 15. The ECU 30calculates the difference (the phase difference) between the angularpositions of the crankshaft 11 and the camshaft 15 which are detected bythe crankshaft position sensor 21 and the camshaft position sensor 22.The calculated phase difference agrees with the actual rotational angleAVTA of the camshaft 15 relative to the crankshaft 11. The ECU 30calculates the target rotational angle AVTT of the camshaft 15 relativeto the crankshaft 11 on the basis of the operating conditions of theengine 10. The ECU 30 calculates a desired drive force to the VTT 50 onthe basis of the difference between the target rotational angle AVTT andthe actual rotational angle AVTA. The desired drive force to the VTT 50is given as a desired control rotational angle. The ECU 30 controls theVTT 50 via the linear solenoid 41 in response to the difference betweenthe target rotational angle AVTT and the actual rotational angle AVTA tomove the actual rotational angle AVTA toward the target rotational angleAVTT. Thus, the VTT 50 is feedback-controlled to equalize the actualrotational angle AVTA and the target rotational angle AVTT. The ECU 30detects the presence and the absence of conditions under which air tendsto enter hydraulic fluid in the VVT 50. When the presence of suchconditions is detected, the ECU 30 corrects the target rotational angleAVTT toward the retarded angle side.

If air enters hydraulic fluid in the VTT 50, the pressure of hydraulicfluid therein tends to be insufficient due to an easy variation involume of the air. It is possible to prevent such an insufficienthydraulic pressure from being diagnosed as a trouble in the feedbackcontrol of the VVT 50 since the ECU 30 corrects the target rotationalangle AVTT toward the retarded angle side in these conditions.

In the valve timing control apparatus of the second embodiment of thisinvention, it is thought that the conditions under which air tends toenter hydraulic fluid in VVT 50 occur during turn of the vehicle. Infact, air tends to enter hydraulic fluid in the VVT 50 and the pressureof hydraulic fluid tends to be unstable during turn of the vehicle. Thetarget rotational angle AVTT is corrected toward the retarded angle sideduring turn of the vehicle. Thus, it is possible to prevent temporarywrong operation of the VTT 50, which is caused by the entry of air intohydraulic fluid, from being diagnosed as a failure of the VTT 50 duringturn of the vehicle.

The valve timing control apparatus of the second embodiment of thisinvention decides that the vehicle is turning in the case where thepower steering switch is in its ON position and the current vehiclespeed exceeds the reference speed KVCIR. Turn of the vehicle may bedetected from other parameters such as the lateral acceleration of thevehicle body which is sensed by a lateral G sensor, the steering angleof the steering wheel, the rotational engine speed, and the engine load.

Third Embodiment

A third embodiment of this invention is similar to the first embodimentthereof except for design changes indicated later.

In the third embodiment of this invention, the ECU 30 operates inaccordance with a program stored in its internal ROM. FIG. 5 is aflowchart of a segment (routine) of the program which is designed todiagnose a trouble in or a failure of the VVT 50. In the case where theengine 10 has four cylinders, the program segment in FIG. 5 is executedfor every 180° CA (crank angle).

As shown in FIG. 5, a first step S301 of the program segment clears thevariable CVDTA to "0". The variable CVDTA is used as an indication ofthe time of continuation or the duration of wrong operation of the VVT50.

A step S302 following the step S301 clears the variable CNEHIGH to "0".The variable CNEHIGH is used as an indication of a count number relatedto the lapse of time after the end of high-speed operation. After thestep S302, the program advances to a step S303.

The step S303 reads the current states of the output signals θ1 and θ2of the crankshaft position sensor 21 and the camshaft position sensor22. The step S303 reads the current value of the rotational engine speedNE (rpm). The step S303 derives the current value of the intake manifoldpressure PM (kgf/cm²) from the output signal of the air pressure sensor.

A step S304 following the step S303 calculates the actual rotationalangle AVTA of the camshaft 15 relative to the crankshaft 11 from thecurrent states of the output signals θ1 and θ2 of the crankshaftposition sensor 21 and the camshaft position sensor 22 by referring toan equation as "AVTA=θ1-θ2".

A step S305 subsequent to the step S304 calculates the target rotationalangle AVTT of the camshaft 15 relative to the crankshaft 11 from thecurrent rotational engine speed NE (rpm) and the current intake manifoldpressure PM (kgf/cm²) as the step S104 in FIG. 2 does.

A step S306 following the step S305 decides whether or not the currentrotational engine speed NE exceeds a predetermined reference speedKVAIR. The reference speed KVAIR is chosen to correspond to a criterionfor a decision regarding whether air tends to enter hydraulic fluid inthe VVT 50. When it is decided that the current rotational engine speedNE exceeds the reference speed KVAIR, or when it is decided that airtends to enter hydraulic fluid in the VVT 50, the program advances fromthe step S306 to a step S307. Otherwise, the program advances from thestep S306 to a step S310.

The step S307 increments a value CVTAIR by "1". The value CVTAIRrepresents the time of continuation or the duration of the high-speedstate.

A step S308 subsequent to the step S307 decides whether or not thehigh-speed continuation time CVTAIR exceeds a predetermined referencetime KVFINH. The reference time KVFINH is chosen to correspond to acriterion for a decision regarding whether air tends to enter hydraulicfluid in the VVT 50. When it is decided that the high-speed continuationtime CVTAIR exceeds the reference time KVFINH, or when it is decidedthat air tends to enter hydraulic fluid in the VTT 50, the programadvances from the step S308 to a step S309. Otherwise, the programadvances from the step S308 to a step S313.

The step S309 sets the count number CNEHIGH to a predetermined numberKNEHIGH corresponding to a predetermined lapse of time after the end ofhigh-speed operation. After the step S309, the current execution cycleof the program segment ends.

Accordingly, in the presence of the conditions under which air tends toenter hydraulic fluid in the VTT 50, main program steps for a troublediagnosis on the VVT 50 remain unexecuted.

The step S310 clears the high-speed duration time CVTAIR to "0".

A step S311 following the step S310 decrements the count number CNEHIGHby "1". As previously indicated, the count number CNEHIGH relates to thelapse of time after the end of high-speed operation.

A step S312 subsequent to the step S311 decides whether or not the countnumber CNEHIGH is equal to "0". In the case where the count numberCNEHIGH is decided to be "0", that is, in the case where it is decidedthat the predetermined time has elapsed since the end of the high-speedoperation, the program advances from the step S312 to the step S313.Otherwise, the program exits from the step S312, and then the currentexecution cycle of the program segment ends.

Accordingly, in the case where the predetermined time has not yetelapsed since the end of the high-speed operation, main program stepsfor a trouble diagnosis on the VVT 50 remain unexecuted.

The step S313 calculates the absolute value |AVTT-AVTA| of thedifference between the actual rotational angle AVTA and the targetrotational angle AVTT which have been given by the steps S304 and S305.The step S313 decides whether or not the absolute value |AVTT-AVTA| ofthe difference exceeds the predetermined reference angular value KVDTA.When it is decided that the absolute value |AVTT-AVTA| of the differenceexceeds the reference angular value KVDTA, the program advances from thestep S313 to a step S314. In this case, it is thought that operation ofthe VVT 50 is wrong. When it is decided that the absolute value|AVTT-AVTA| of the difference does not exceed the reference angularvalue KVDTA, the program returns from the step S313 to the step S301. Inthis case, it is thought that operation of the VVT 50 is good.

The step S314 increments the wrong-operation continuation time CVDTA by"1". After the step 3314, the program advances to a step S315.

The step S315 decides whether or not the wrong-operation continuationtime CVDTA exceeds the predetermined reference time KTDTA. When it isdecided that the wrong-operation continuation time CVDTA exceeds thereference time KTDTA, the program advances from the step S315 to a stepS316. When it is decided that the wrong-operation continuation timeCVDTA does not exceed the reference time KTDTA, the program returns fromthe step S315 to the step S303.

The step S316 sets a flag for indicating that the VVT 50 fails. Inaddition, the step S316 activates the warning lamp. After the step S316,the current execution cycle of the program segment ends.

In the valve timing control apparatus of the third embodiment of thisinvention, it is thought that the conditions under which air tends toenter hydraulic fluid in VVT 50 occur when the rotational engine speedNE exceeds the reference speed KVAIR and the high-speed continuationtime CVTAIR exceeds the reference time KVFINH. Also, the conditionsunder which air tends to enter hydraulic fluid in VVT 50 are thought tobe present in the case where the predetermined time given by the countnumber CNEHIGH has not yet elapsed since the end of the high-speedoperation. In fact, hydraulic fluid fed to the VVT 50 tends to beatomized and hence air tends to enter hydraulic fluid in the VVT 50until the predetermined time has elapsed since the end of the high-speedoperation. After the predetermined time has elapsed since the end of thehigh-speed operation, the atomization of the hydraulic fluid disappears.The execution of the trouble diagnosis on the VTT 50 is inhibited whenthe rotational engine speed NE exceeds the reference speed KVAIR and thehigh-speed continuation time CVTAIR exceeds the reference time KVFINH.Also, the execution of the trouble diagnosis on the VTT 50 is inhibitedin the case where the predetermined time has not yet elapsed since theend of the high-speed operation. Thus, it is possible to preventtemporary wrong operation of the VIT 50, which is caused by the entry ofair into hydraulic fluid, from being diagnosed as a failure of the VTT50 under these conditions.

Fourth Embodiment

A fourth embodiment of this invention is similar to the first embodimentthereof except for design changes indicated later.

In the fourth embodiment of this invention, the ECU 30 operates inaccordance with a program stored in its internal ROM. FIG. 6 is aflowchart of a segment (routine) of the program which is designed todetect, in response to a hydraulic pressure, the occurrence ofconditions where air tends to enter hydraulic fluid in the VVT 50. Inthe case where the engine 10 has four cylinders, the program segment inFIG. 6 is executed for every 180° CA (crank angle).

As shown in FIG. 6, a first step S401 of the program segment clears thevariable POILUP to "0". The variable POILUP is used as an indication ofa count number related to conditions in which the pressure of hydraulicfluid in the VVT 50 is normal.

A step S402 following the step S401 clears the variable COILUP to "0".The variable COILUP is used as an indication of a count number relatedto a time interval for a decision regarding whether the pressure ofhydraulic fluid is normal or abnormal. After the step S402, the programadvances to a step S403.

The step S403 derives the current value Poil of the actual pressure ofhydraulic fluid from the output signal of the hydraulic pressure sensor49. The actual hydraulic pressure Poil is equal to the pressure at theoutlet of the pump 46. The step S403 reads the current value of therotational engine speed NE. The step S403 determines a target hydraulicpressure TPOILUP on the basis of the current rotational engine speed NE.

The ROM in the ECU 30 stores information of a map which indicates apredetermined relation between the target hydraulic pressure TPOILUP andthe rotational engine speed NE. An example of the map is shown in FIG.7. The step S403 implements the determination of the target hydraulicpressure TPOILUP by referring to the map in FIG. 7.

The step S403 decides whether or not the actual hydraulic pressure Poilexceeds the target hydraulic pressure TPOILUP. When it is decided thatthe actual hydraulic pressure Poil exceeds the target hydraulic pressureTPOILUP, the program advances from the step S403 to a step S404. In thiscase, the pressure of hydraulic pressure in the VVT 50 is thought to benormal. When it is decided that the actual hydraulic pressure Poil doesnot exceed the target hydraulic pressure TPOILUP, the program jumps fromthe step S403 to a step S405.

The step S404 increments the count number POILUP by "1". As previouslyindicated, the count number POILUP is related to the conditions in whichthe pressure of hydraulic fluid in the VVT 50 is normal. After the stepS404, the program advances to the step S405.

The step S405 increments the count number COILUP by "1". As previouslyindicated, the count number COILUP is related to the time interval forthe decision regarding whether the pressure of hydraulic fluid is normalor abnormal.

A step S406 following the step S405 compares the count number COILUPwith a predetermined reference number KTOILUP corresponding to apredetermined time interval for the decision regarding whether thepressure of hydraulic fluid is normal or abnormal. When it is decidedthat the count number COILUP is equal to or greater than the referencenumber KTOILUP, the program advances from the step S406 to a step S407.Otherwise, the program returns from the step S406 to the step S403.

The step S407 compares the count number POILUP with a predeterminedreference number KPOILUP. The reference number KPOILUP is chosen tosatisfy the following condition. In the case where the pressure ofhydraulic fluid in the VVT 50 remains normal, the count number POILUPwhich relates to the normality of the hydraulic pressure will reach thereference number KPOILUP in the predetermined time interval given by thereference number KTOILUP. When it is decided that the count numberPOILUP is equal to or greater than the reference number KPOILUP, theprogram advances from the step S407 to a step S408. When it is decidedthat the count number POILUP is smaller than the reference numberKPOILUP, the program advances from the step S407 to a step S409.

The step S408 decides that the conditions under which air tends to enterhydraulic fluid in the VVT 50 are absent. The step S408 subjects the VVT50 to processes designed for normal operation of the VVT 50. After thestep S408, the current execution cycle of the program segment ends.

The step S409 decides that the conditions under which air tends to enterhydraulic fluid in the VVT 50 are present. The step S409 inhibits thetrouble diagnosis on the VTT 50 from being implemented as in the firstembodiment of this invention. Alternatively, the step S409 may correctthe target rotational angle AVTT toward the retarded angle side as inthe second embodiment of this invention. After the step S409, thecurrent execution cycle of the program segment ends.

In the valve timing control apparatus of the fourth embodiment of thisinvention, the decision regarding the presence and the absence of theconditions under which air tends to enter hydraulic fluid in VVT 50 isimplemented on the basis of the pressure of hydraulic fluid. When thepressure of hydraulic fluid fed to the VVT 50 is abnormal, there is ahigh chance of the entry of air into hydraulic fluid. Accordingly, it isthought that the conditions under which air tends to enter hydraulicfluid in VVT 50 occur when the pressure of hydraulic fluid is abnormal.The execution of the trouble diagnosis on the VTT 50 is inhibited or thetarget rotational angle AVTT is corrected toward the retarded angle sidewhen the pressure of hydraulic fluid is abnormal. Thus, it is possibleto prevent temporary wrong operation of the VTT 50, which is caused bythe entry of air into hydraulic fluid, from being diagnosed as a failureof the VTT 50 under these conditions.

Fifth Embodiment

A fifth embodiment of this invention is similar to the first embodimentthereof except for design changes indicated later.

In the fifth embodiment of this invention, the ECU 30 operates inaccordance with a program stored in its internal ROM. FIG. 8 is aflowchart of a segment (routine) of the program which is designed todetect, in response to vehicle traveling conditions, the occurrence ofconditions where air tends to enter hydraulic fluid in the VVT 50. Inthe case where the engine 10 has four cylinders, the program segment inFIG. 8 is executed for every 180° CA (crank angle).

As shown in FIG. 8, a first step S501 of the program segment reads thecurrent time tl80i during which the crankshaft 11 rotates through 180°CA (crank angle). The step S501 stores information of the current timetl80i into the RAM within the ECU 30 for later use.

A step S502 following the step S501 calculates a time difference Δtequal to the current time tl80i minus the previous time tl80i-2 given bythe step S501 in the execution cycle of the program segment whichsecond-immediately precedes the current execution cycle of the programsegment. The vehicle can be decided to be traveling on a rough road ifthe time difference Δt is outside a given range.

A step S503 subsequent to the step S502 decides whether or not the timedifference Δt is between a predetermined lower limit value KDRAFL and apredetermined upper limit value KDRAFH. When the time difference Δt isbetween the lower limit value KDRAFL and the upper limit value KDRAFH,it is decided that the vehicle is travelling on a flat road. In thiscase, the conditions under which air tends to enter hydraulic fluid inthe VVT 50 are decided to be absent, and the program advances from thestep S503 to a step S504. When the time difference At is not between thelower limit value KDRAFL and the upper limit value KDRAFH, it is decidedthat the vehicle is travelling on a rough road. In this case, theconditions under which air tends to enter hydraulic fluid in the VVT 50are decided to be present, and the program advances from the step S503to a step S505.

The step S504 confirms that the conditions under which air tends toenter hydraulic fluid in the VVT 50 are absent. The step S504 subjectsthe VVT 50 to processes designed for normal operation of the VVT 50.After the step S504, the current execution cycle of the program segmentends.

The step S505 confirms that the conditions under which air tends toenter hydraulic fluid in the VVT 50 are present. The step S505 inhibitsthe trouble diagnosis on the VVT 50 from being implemented as in thefirst embodiment of this invention. Alternatively, the step S505 maycorrect the target rotational angle AVTT toward the retarded angle sideas in the second embodiment of this invention. After the step S505, thecurrent execution cycle of the program segment ends.

In the valve timing control apparatus of the fifth embodiment of thisinvention, it is thought that the conditions under which air tends toenter hydraulic fluid in VVT 50 occur when the vehicle is traveling on arough road. In fact, the level of hydraulic fluid fed to the VVT 50 isunstable and hence air tends to enter hydraulic fluid when the vehicleis traveling on a rough road. The execution of the trouble diagnosis onthe VTT 50 is inhibited or the target rotational angle AVTT is correctedtoward the retarded angle side when the vehicle is traveling on therough road. Thus, it is possible to prevent temporary wrong operation ofthe VTT 50, which is caused by the entry of air into hydraulic fluid,from being diagnosed as a failure of the VTT 50 under these conditions.

The valve timing control apparatus of the fifth embodiment of thisinvention decides whether the vehicle is traveling on a rough road or aflat road on the basis of a change in the time tl80 during which thecrankshaft 11 rotates through 180° CA (crank angle). The decisionregarding whether the vehicle is traveling on a rough road or a flatroad may be implemented on the basis of the output signal of a G sensorfor detecting the acceleration of the vehicle body, the output signal ofa height sensor for detecting the relative distance between the vehiclewheels and the vehicle body, or the output signals of sensors fordetecting the rotational speeds of the vehicle wheels.

Sixth Embodiment

With reference to FIG. 9, a valve timing control apparatus of a sixthembodiment of this invention operates for an internal combustion engine110 having a crankshaft 111 which serves as a driving shaft with respectto a variable valve timing control mechanism 150. The valve timingcontrol apparatus contains the variable valve timing control mechanism150.

The crankshaft 111 is connected to a pair of chain sprockets 113 and 114via a chain 112 in the valve timing control apparatus. A drive force canbe transmitted from the crankshaft 111 to the chain sprockets 113 and114. As the crankshaft 111 rotates, the chain sprockets 113 and 114 alsorotate. Generally, the rotational speed of the chain sprockets 113 and114 is equal to half the speed of rotation of the crankshaft 111. Thechain sprocket 113 is connected to a camshaft 115 for drivingengine-cylinder inlet valves (not shown). Normally, the camshaft 115rotates together with the chain sprocket 113. The camshaft 115 serves asa driven shaft with respect to the variable valve timing controlmechanism 150. The chain sprocket 114 is mounted on a camshaft 116 fordriving engine-cylinder outletvalves (not shown). The camshaft 116rotates together with the chain sprocket 114.

A crankshaft position sensor 121 is associated with the crankshaft 111.The crankshaft position sensor 121 outputs a pulse signal θ1representing the angular position of the crankshaft 111. A camshaftposition sensor 122 is associated with the camshaft 115. The camshaftposition sensor 122 outputs a pulse signal θ2 representing the angularposition of the camshaft 115.

An electronic control unit (ECU) 130 receives the output signals θ1 andθ2 of the crankshaft position sensor 121 and the camshaft positionsensor 122. The ECU 130 includes a microcomputer or a logic operationcircuit having a combination of a CPU, a ROM, a general RAM, a backupRAM, an input/output port, and bus lines. The ECU 130 operates inaccordance with a program stored in the ROM.

The engine 110 has an exhaust passage 190 which can communicate with theengine cylinders via the engine-cylinder outlet valves. A three-waycatalytic converter 180 is disposed in the exhaust passage 190. A frontO₂ sensor 160 is located in a region of the exhaust passage 190 upstreamof the three-way catalytic converter 180. The front O₂ sensor 160 isexposed to exhaust gas, and outputs a signal to the ECU 130 whichrepresents the O₂ concentration of the exhaust gas. A rear O₂ sensor 170is located in a region of the exhaust passage 190 downstream of thethree-way catalytic converter 180. The rear O₂ sensor 170 is exposed toexhaust gas, and outputs a signal to the ECU 130 which represents the O₂concentration of the exhaust gas.

The engine 110 is provided with a known fuel vapor treating apparatus(not shown) including a canister. Fuel vapor generated in a fuel tank isabsorbed by the canister, being transmitted from the canister to an airintake passage of the engine 110.

An air flow meter (not shown) detects the rate GN of air flow into theengine cylinders. The ECU 130 receives an output signal of the air flowmeter which represents the detected air flow rate GN.

A temperature sensor (not shown) detects the temperature of coolant inthe engine 110. The ECU 130 receives an output signal of the temperaturesensor which represents the detected engine coolant temperature.

The ECU 130 calculates an actual rotational angle AVTA of the camshaft115 relative to the crankshaft 111 on the basis of the output signals θ1and θ2 of the crankshaft position sensor 121 and the camshaft positionsensor 122. In addition, the ECU 130 calculates a target rotationalangle AVTT of the camshaft 115 relative to the crankshaft 111 on thebasis of the output signals of sensors including the crankshaft positionsensor 121 and the air flow meter. Furthermore, the ECU 130 calculatesthe rotational engine speed NE, that is, the speed of rotation of thecrankshaft 111 on the basis of the output signal θ1 of the crankshaftposition sensor 121.

A spool valve 140 which serves as an oil-flow control valve (OCV) can beactuated by a linear solenoid 141. The spool valve 140 is disposed inhydraulic passages extending among a tank 145, a pump 146, and thevariable valve timing control mechanism (VVT) 150. The tank 145 containshydraulic fluid. The pump 146 draws hydraulic fluid from the tank 145,and pumps hydraulic fluid toward the VVT 150 via a fluid feed passage147 and the spool valve 140. The state or the position of the spoolvalve 140 is controlled by the linear solenoid 141. The spool valve 140can adjust the rate of hydraulic-fluid flow to the VVT 150 in responseto the duty cycle or the duty factor of a drive pulse signal applied tothe linear solenoid 141. The VVT 150 is provided between the chainsprocket 113 and the camshaft 115. The VVT 150 varies the angulardifference (the phase difference) between the sprocket 113 and thecamshaft 115, that is, the rotational angle of the camshaft 115 relativeto the crankshaft 111 in response to hydraulic fluid fed via the spoolvalve 140. Hydraulic fluid can return from the VVT 150 to the tank 145via the spool valve 140 and a fluid return passage 148.

The ECU 130 calculates the difference between the actual rotationalangle AVTA and the target rotational angle AVTT of the camshaft 115relative to the crankshaft 111. The ECU 130 generates a fixed-frequencydrive pulse signal for the linear solenoid 141 which has a duty cycle ora duty factor depending on the calculated difference between the actualrotational angle AVTA and the target rotational angle AVTT of thecamshaft 115 relative to the crankshaft 111. Thereby, the actualrotational angle AVTA of the camshaft 115 relative to the crankshaft 111can be equalized to the target rotational angle AVTT thereof.

The crankshaft position sensor 121 and the camshaft position sensor 122are designed to implement the following processes. During everyrevolution of the crankshaft 111, N pulses are successively outputtedfrom the crankshaft position sensor 121. Here, N denotes a predeterminednatural number. During every revolution of the camshaft 115, N pulsesare successively outputted from the camshaft position sensor 122. Thenumber N is chosen to satisfy a condition as "N<360/θmax" where θmaxdenotes the maximum value of timing conversion related to the camshaft115 which is expressed in unit of degree in crank angle (CA).Accordingly, a pulse in the output signal θ1 of the crankshaft positionsensor 121, and a pulse in the output signal θ2 of the camshaft positionsensor 122 which occurs immediately after the pulse in the signal θ1 canbe used in calculating the actual rotational angle AVTA of the camshaft115 relative to the crankshaft 111.

As previously explained, the ECU 130 operates in accordance with aprogram stored in its internal ROM. FIG. 10 is a flowchart of a segment(routine) of the program which is designed to control the duty cycle ofthe drive pulse signal fed to the linear solenoid 141. The programsegment in FIG. 10 is executed for every given time interval.

As shown in FIG. 10, a first step S601 of the program segment reads thecurrent states of the output signals θ1 and θ2 of the crankshaftposition sensor 121 and the camshaft position sensor 122. The step S601reads the current value of the rotational engine speed NE. The step S601derives the current value GN of the air flow rate from the output signalof the air flow meter.

A step S602 following the step S601 calculates the actual rotationalangle AVTA of the camshaft 115 relative to the crankshaft 111 from thecurrent states of the output signals θ1 and θ2 of the crankshaftposition sensor 121 and the camshaft position sensor 122 by referring toan equation as "AVTA=θ1-θ2".

A step S603 subsequent to the step S602 calculates the target rotationalangle AVTT of the camshaft 115 relative to the crankshaft 111 from thecurrent rotational engine speed NE and the current air flow rate GN.

The ROM in the ECU 130 stores information of a table map which indicatesa predetermined relation among the target rotational angle AVTT, therotational engine speed NE, and the air flow rate GN. An example of thetable map is shown in FIG. 11. The step S603 implements the calculationof the target rotational angle AVVT by referring to the table map inFIG. 11.

A step S604 following the step S603 calculates a rotational angledifference which is equal to the target rotational angle AVTT minus theactual rotational angle AVTA. The step S604 determines a controlrotational angle DVFB on the basis of the calculated rotational angledifference "AVTT-AVTA". The control rotational angle DVFB corresponds toa feedback corrective quantity.

The ROM in the ECU 130 stores information of a map which indicates apredetermined relation between the control rotational angle DVFB and therotational angle difference "AVTT-AVTA". An example of the map is shownin FIG. 12. The step S604 implements the determination of the controlrotational angle DVFB by referring to the map in FIG. 12.

A step S605 subsequent to the step S604 calculates a desired duty cycleDV of the drive pulse signal to the linear solenoid 141 from the controlrotational angle DVFB and a basic duty value DVT according to thefollowing equation.

    DV=DVT+DVFB

The basic duty value DVT is a term for maintaining the actual rotationalangle AVTA at the current value. As shown in FIG. 13, the rate ofhydraulic fluid flow into the VVT 150 depends on the desired duty cycleDV or the basic duty value DVT.

In other words, the step S605 corrects and updates the desired dutycycle DV in response to the control rotational angle DVFB according to aprogram statement as "DV=DV+DVFB".

The step S605 outputs a drive pulse signal to the linear solenoid 141which has a duty cycle equal to the desired duty cycle DV. After thestep S605, the current execution cycle of the program segment ends andthe program returns to the main routine.

According to the program segment in FIG. 10, the valve timing controlapparatus enables the actual rotational angle AVTA to follow the targetrotational angle AVTT. Thus, the valve timing control apparatus can bedecided to be wrong in the case where the actual rotational angle AVTAcontinues to differ from the target rotational angle AVTT by a givenvalue or more during at least a given time interval.

FIG. 14 is a flowchart of another segment (routine) of the program forthe ECU 130 which is designed to diagnose a trouble in or a failure ofthe valve timing control apparatus. In the case where the engine 110 hasfour cylinders, the program segment in FIG. 14 is executed for every180° CA (crank angle).

As shown in FIG. 14, a first step S701 of the program segment reads thecurrent value of the target rotational angle AVTT, the current value ofthe actual rotational angle AVTA, and a predetermined reference value"k".

A step S702 calculates the absolute value |AVTT-AVTA| of the differencebetween the actual rotational angle AVTA and the target rotational angleAVTT which have been read by the step S701. The step S702 decideswhether or not the absolute value |AVTT-AVTA| of the difference exceedsthe reference value "k". When it is decided that the absolute value|AVTT-AVTA| of the difference exceeds the reference value "k", theprogram advances from the step S702 to a step S703. Otherwise, theprogram advances from the step S702 to a step S705.

The step S703 decides whether or not a predetermined time interval haselapsed since the moment at which the absolute value |AVTT-AVTA| of thedifference starts to exceed the reference value "k". When it is decidedthat the predetermined time interval has elapsed, the program advancesfrom the step S703 to a step S704. In this case, it is thought that thevalve timing control apparatus is wrong. When it is decided that thepredetermined time interval has not yet elapsed, the program advancesfrom the step S703 to the step S705.

The step S704 sets an abnormality indication flag XVVT to "1". After thestep S704, the current execution cycle of the program segment ends andthe program returns to the main routine.

The step S705 sets the abnormality indication flag XVVT to "0". Afterthe step S705, the current execution cycle of the program segment endsand the program returns to the main routine.

The ECU 130 is connected to an ignition device (not shown) of the engine110. The ECU 130 adjusts the ignition device to control a spark timingin the engine 110.

FIG. 15 is a flowchart of still another segment (routine) of the programfor the ECU 130 which is designed to control a spark timing in theengine 110 and to implement various malfunction detection processes. Theprogram segment in FIG. 15 is executed for every given crank angle.

As shown in FIG. 15, a first step S801 of the program segment decideswhether or not the abnormality indication flag XVVT is equal to "0".When it is decided that the abnormality indication flag XVVT is equal to"0", that is, when it is decided that the valve timing control apparatusis normal, the program advances from the step S801 to a block S802.Otherwise, the program advances from the step S801 to a block S808.

The block S802 implements a misfire detection process related to theengine 110.

A block S803 following the block S802 implements a process of detectingmalfunction of a fuel supply apparatus of the engine 110.

A block S804 subsequent to the block S803 implements a process ofdetecting malfunction of the front O₂ sensor 160, and also a process ofdetecting malfunction of the rear O₂ sensor 170.

A block S805 following the block S804 implements a process of detectingdeterioration of the three-way catalytic converter 180.

A block S806 subsequent to the block S805 implements a process ofdetecting malfunction of the fuel vapor treating apparatus.

A block S807 following the block S806 executes feedback control of thespark timing in response to knocking conditions in the engine 110. Afterthe block S807, the current execution cycle of the program segment endsand the program returns to the main routine.

The block S808 implements a fail-safe process. After the block S808, thecurrent execution cycle of the program segment ends and the programreturns to the main routine.

The engine 110 is provided with various devices and apparatuses whichmight be adversely affected by wrong operation of the valve timingcontrol apparatus. The fail-safe process implemented by the block S808includes a step of inhibiting trouble diagnoses on these devices andapparatuses. The fail-safe process also includes a step of interruptingthe knocking-based feedback control of the spark timing, and a step offorcedly setting the spark timing to the most retarded timing (theretarded-side limit timing).

If the valve timing control apparatus fails, the valve timing is wrongand hence operation of the engine 110 is unstable. Especially, if thevalve timing control apparatus fails at an advanced spark timing and ata low engine load, the valve overlap is large and thus the burning inthe engine 10 is impaired so that misfire tends to occur. If the misfireis detected and parts of the engine 110 are erroneously decided to bewrong, some of good parts may be replaced although only the valve timingcontrol apparatus is wrong. Accordingly, when malfunction of the valvetiming control apparatus is detected, the misfire detection process isinterrupted by the block S808 to prevent erroneous replacement of goodparts.

If the valve timing control apparatus fails, the burning in the engine110 is impaired. In this case, the burning in the engine 110 is notimproved although the ECU 130 feeds a proper feedback control signal tothe fuel supply apparatus. Thus, in this case, the fuel supplyapparatus, the front O₂ sensor 160, the rear O₂ sensor 170, and thethree-way catalytic converter 180 might be erroneously decided to bewrong. Accordingly, when malfunction of the valve timing controlapparatus is detected, the process of detecting malfunction of the fuelsupply apparatus of the engine 110, the process of detecting malfunctionof the front O₂ sensor 160, the process of detecting malfunction of therear O₂ sensor 170, and the process of detecting deterioration of thethree-way catalytic converter 180 are interrupted by the block S808 toprevent erroneous decisions.

The process of detecting malfunction of the fuel vapor treatingapparatus includes a step of deciding whether or not a vacuum can benormally introduced into the fuel vapor treating apparatus from the airintake passage of the engine 110. If a hole is made in the fuel vaportreating apparatus, a vacuum can not be normally introduced into thefuel vapor treating apparatus since the vacuum escapes from the hole. Ifthe valve timing control apparatus fails, the burning is impaired andthe pressure in the air intake passage of the engine 110 rises. Thus, inthis case, since a vacuum can not be normally introduced into the fuelvapor treating apparatus, the fuel vapor treating apparatus may beerroneously decided to be wrong. Accordingly, when malfunction of thevalve timing control apparatus is detected, the process of detectingmalfunction of the fuel vapor treating apparatus is interrupted by theblock S808 to prevent an erroneous decision.

If the valve timing control apparatus fails, the valve timing is wrongand the charging efficiency varies so that the spark timing is improper.At intermediate and heavy engine loads, the variable valve timingcontrol mechanism 150 is set to an advanced angle side to meetrequirements related to fuel economy and emission control. If thevariable valve timing control mechanism 150 is set to an advanced angleside, the internal EGR (exhaust gas recirculation) rate increases andhence the knock limit of the spark timing shifts toward an advancedangle side. If the variable valve timing control mechanism 150 is fixedto a retarded angle side due to malfunction of the valve timing controlapparatus, the knock limit is in a retarded angle side so that knockingtends to occur. Accordingly, when malfunction of the valve timingcontrol apparatus is detected, the block S808 interrupts theknocking-based feedback control of the spark timing, and forcedly setsthe spark timing to the most retarded timing (the retarded-side limittiming).

It should be noted that when malfunction of the valve timing controlapparatus is detected, the knocking-based feedback control of the sparktiming may be held active. In this case, it is preferable that theknocking-based feedback control of the spark timing is made moresensitive by increasing a retardation angle quantity of the feedbackgain.

As previously explained, when the valve timing control apparatus fails,the various trouble diagnoses or the various abnormality detectionprocesses are interrupted to prevent wrong diagnoses or wrongdetections. Thus, it is possible to prevent good parts from beingerroneously replaced. The prevention of wrong diagnoses or wrongdetections results in increases in the reliabilities of the varioustrouble diagnoses or the various abnormality detection processes. Whenthe valve timing control apparatus fails, the spark timing is forcedlyset to the most retarded timing (the retarded-side limit timing). Thus,it is possible to prevent the occurrence of knocking, and to protect theengine 110.

The valve timing control apparatus may be of another type such as thecam change type, the lift amount variable time, or the cam phase/liftamount variable type. The method of detecting malfunction of the valvetiming control apparatus may be replaced by another method.

Trouble diagnoses or abnormality detection processes on other devicesmay be interrupted when the valve timing control apparatus fails. Forexample, an abnormality detection process on the crankshaft positionsensor 121 or the camshaft position sensor 122 may be interrupted. Atleast one of the trouble diagnoses or the abnormality detectionprocesses may be interrupted.

The results of the abnormality detections may be invalidated instead ofinterrupting the abnormality detection processes. Specifically, in thecase where the step S801 decides the abnormality indication flag XVVT tobe equal to "1", the abnormality detection processes on the variousdevices and apparatuses are continued and the results of the abnormalitydetections are invalidated. The abnormality detection processes may besubstantially disabled by relaxing the criteria for the decisionsregarding whether the devices and apparatuses are normal or abnormal.

What is claimed is:
 1. A valve timing control apparatus for an internalcombustion engine, comprising:a variable valve timing control mechanismof a hydraulic type which is provided in a drive force transmissionarrangement for transmitting a drive force from a driving shaft to adriven shaft for actuating one of an engine-cylinder inlet valve and anengine-cylinder outlet valve, and which can relatively rotate one of thedriving shaft and the driven shaft in a predetermined angular range;detecting means for detecting a condition in which air enters hydraulicworking fluid in the variable valve timing control mechanism; troublediagnosis means for implementing a trouble diagnosis on the variablevalve timing control mechanism; and inhibiting means for inhibiting thetrouble diagnosis implemented by the trouble diagnosis means when thedetecting means detects the condition in which air enters hydraulicworking fluid in the variable valve timing control mechanism.
 2. A valvetiming control apparatus according to claim 1, furthercomprising:driving shaft rotational angle detecting means for detectinga rotational angle of the driving shaft; driven shaft rotational angledetecting means for detecting a rotational angle of the driven shaft;relative rotational angle calculating means for calculating an actualrelative rotational angle which is equal to an actual phase differencebetween the rotational angle of the driving shaft which is detected bythe driving shaft rotational angle detecting means and the rotationalangle of the driven shaft which is detected by the driven shaftrotational angle detecting means; engine operating condition detectingmeans for detecting an operating condition of the engine; targetrelative rotational angle calculating means for calculating a targetrelative rotational angle which is equal to a target phase differencebetween the rotational angle of the driving shaft and the rotationalangle of the driven shaft in response to the operating condition of theengine which is detected by the engine operating condition detectingmeans; control rotational angle calculating means for calculating acontrol rotational angle in response to a difference between the actualrelative rotational angle calculated by the relative rotational anglecalculating means and the target relative rotational angle calculated bythe target relative rotational angle calculating means; and relativerotational angle control means for controlling the variable valve timingcontrol mechanism to relatively rotate one of the driving shaft and thedriven shaft in response to the control rotational angle calculated bythe control rotational angle calculating means.